The pathogenesis of retinal neovascularization in ROP is incompletely understood, although hypoxia is thought to be critical for its development. The long-term objective of this research is to understand better the role of hypoxia in retinal neovascularization so that more effective preventative, diagnostic and therapeutic strategies may be developed. During the previous funding period a novel MRI method was developed to non-invasively map the oxygenation rate along the two-dimensional extent of the retina. This method showed that an unusually slow retinal oxygenation rate was present in retinas before the development of ROP. This slow oxygenation rate is consistent with hypoxia, but it cannot yet be interpreted unambiguously as a measure of hypoxia. The present proposal seeks to confirm two hypotheses: (1) that abnormally slow oxygenation provides an indirect, yet specific measure of hypoxia and (2) that this MRI method has potential clinical utility for directing supplemental oxygen therapy. Three specific aims will be addressed using this MRI method and a newborn rat model of ROP: (1) to determine the association between the preretinal vitreous retinal oxygen tension and oxygenation rate under normal and pathological conditions; (2) to determine if the change in retinal oxygenation that occurs during supplemental oxygen treatment is linear with supplemental dose and evolves during neovascularization; and (3) to determine the association between the retinal oxygenation rate measured before neovascularization and the level of supplemental oxygen needed to prevent vascular endothelial growth factor (VEGF) upregulation and neovascularization. The proposed studies will lay the groundwork for eventual clinical evaluation of similar MRI experiments in human ROP. This work may have broad impact beyond ROP since abnormal blood vessel growth is a common pathobiologic event for other blinding disorders, such as diabetic retinopathy.